1. Week 6: (March 15, 2011) Auditory Maps and orienting: need for Coordinate Transformations

2. The Barnowl (tyto alba): Ears are placed asymmetrically View on left side View on right side

3. (Takahashi) Convergence of many ICc neurons onto a single ICx neuron creates ITD sensitivity

4. (Takahashi) Neurons in the owl’s ventral lemniscus are sensitive to the interaural level difference (ILD)! (equivalent to the LSO in mammals)

5. (Knudsen/Konishi) Formation of a space-specific neuron in the owl’s ICx: Convergence of ITD and ILD sensitive neurons

6. The neural map of auditory space in the owl’s ICx The formation of this computational map depends critically on the quality of the owl’s visual system through feedback connections from the SC (later.....).

7. General Organization of the Mammalian Auditory System ACOUSTIC subcortical pathways I

8. The Direct Sound-Localization and Orienting Pathway: Superior Colliculus: eye-head orienting Inferior Colliculus: sound direction Brainstem: acoustic cue processing

9. Orienting of eyes, head, body (and pinnae) involves the midbrain Superior Colliculus (SC): SC EYE HEAD VISION AUDITION SC: - Multisensory - Sensorimotor ‘interface’ - Topographic map of saccadic gaze shifts ‘sensory’ motor

10. SC: Topographic map of gaze - shifts: saccade vectors time Firing rate Hor. Eye Pos Vert. Eye Pos Hor. Eye Pos Independent of eye position

11. Making an eye movement towards a sound requires a coordinate transformation: This transformation necessiates a signal about eye position re. head, E

12. C HE V AV’ Eye and Head Not Aligned 20-20 20 HE AV Eye and Head Aligned A 2 5 10 20 40 0 -30 30 -60 up down rostral caudal V A B 2 5 10 20 40 0 -30 30 -60 up down rostral caudal V A D V’V’V’V’ A’A’A’A’

13. Jay and Sparks (1984/1987): Auditory respon- ses in SC are eye-centered in eye-centered coordinates coordinates. Question: How do these cells get their information? Hypothesis: The midbrain IC could convey this signal.

14. Tuning of an IC neuron to eye position. 1. FR increases for rightward eye fixations. 2. FR increases only during the acoustic response: “GAIN FIELD”

15. Neural Network Model of IC-SC mapping Sound level and sound position modulation Activity of model IC neurons: are randomly distributed across the IC population (240 IC neurons, 12 freq bands; 100 SC neurons in map). PeakGaussian Tuning Curve Eye position modulation Brainstem pathways Topographic code of eye-motor error Tonotopic code of sounds SC IC HRTF/ILD sound at (AZ,EL) freq Eye position Up Down Hor

16. Example of a typical IC model neuron: ‘gain field’

17. Simulation result for T H =(+20,+30)deg and E H =(-30,+30) => M E = (50,0) M H E M = H-E T O F

18. OMR + + + Body Head Eye Target Audition: Target re. Head Vision: Target re. Eye Somatosensation: Target re. Body Eye re. Head Head re. Body Reference frames: including the head and body Eye movements require oculocentric error signalsHead movements require craniocentric error signals Vision is Eye-Centered Audition is Head-Centered

19. head-free In head-free orienting(human): Eyes Eyes(Go)and head head(Ho)indeed both move both toward a visual or auditory target. Goossens & Van Opstal, Exp. Brain Research, 114 (1997)

20. Studying coordinate transformations - I: Does the auditory system keep sounds in head-centered coordinates? First, the rationale behind the underlying idea: “the double-step paradigm and pure-tone localization” Goossens and Van Opstal, J Neurophysiol 1999

21. Studying coordinate transformations - I Goossens & Van Opstal, J Neurophysiol 1999 Double-Step Paradigm Pure-Tone Localization Paradigm

22. (V) (S) The sound-localization system should be able to account for intervening movements of the eyes and head: S THTH S F Azimuth Elevation Gaze shift ∆G GSGS GHGH V G H =T H G S =T H - ∆G

23. Sound localization responses are spatially accurate (Goossens and Van Opstal, 1999)

24. Pure-Tone Localization Behaviour: do head movements help?

25. Pure-Tone Localization: (in)dependent of head orientation?

26. Pure-Tone Localization: depends on head orientation AND on tone frequency!

27. Sounds appear to be represented in a spatial (body-centered) reference frame (T SPACE = T HEAD +H SPACE ): Computation WITHIN the (tonotopic) auditory system

28. Dynamic coordinate transformations for multisensory orienting: